An integrated circuit (IC) is an electronic circuit manufactured into the surface of a thin substrate of semiconductor material. ICs are used in virtually all electronic equipment today and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the low cost of producing ICs.
An IC is assembled into a package. The IC package protects the IC die from physical damage and redistributes the I/O to a more manageable pitch in assembly. An IC package also performs other functions such as providing a structure more amenable to standardization, providing a thermal path away from the die, providing protection from the potential of soft errors due to alpha particles, and providing a structure more easily disposed to electrical test and burn-in. Some current IC package technologies include quad flat pack (QFP), pin grid array (PGA), ball grid array (BGA), flip chips (FC), three dimensional integrated circuits (3DIC), chip scale packages, and package on package (PoP) devices.
A packaged device is then attached to a printed circuit board (PCB). A PCB is used as a base frame to mechanically support and electrically connect electronic components such as IC packages using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. Surface-mount technology (SMT) is a method for constructing electronic circuits in which an IC package is mounted directly onto the surface of PCBs. In SMT, components such as IC packages are placed on PCB contact pads and then electrically and mechanically coupled to the PCB with connectors such as solder balls.
There are a variety of techniques used to attach components such as IC packages to PCBs. However, current techniques of connecting the connectors and PCB contact pads or pre-solder may have some acute angles between connectors and PCB contact pads resulting in non-smooth joints, due to the notch stress concentration between the connectors and PCB contact pads. The acute angles may lead to ball crack points between the connectors and PCB contact pads connections. Molding compound alone may not be able to effectively reduce the crack points. Methods and apparatus are needed to attach IC packages to PCBs to form smooth solder joints.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.